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Hi Matthew
my 2 bobs worth, running a HEQ5 mount on battery power :
My current setup uses a SCA 1900 'jump start' unit which reputedly has a 30+ AmpHr battery and certainly feels heavy enough.
Its weight is actually useful as I hang it from a hook under the centre post. In that way, it provides the tripod with extra mass and stability. (and on those public nights when the visitors kick the tripod : nothing moves ! )
I also added a 'merit' plug which offers more positive connection than a ciggie lighter, and I also secure the cable so there is no weight or pull on the HEQ5 socket when the mount slews. I also used heavier duty flexible cable to minimise voltage drop when slewing.
The big battery also offers enough capacity to run a 12V hair dryer for a few minutes as occasionally required. I do 'park' the scope first though, but leave the power on. By the time I have put the dryer away, the voltage has recovered enough to use the mount again, and I can re-slew to the last target. ( A small battery would be trashed quickly with such a 15Amp drain, however short.)
The battery is also fairly new so I have no idea of its potential life. It was cheap enough in the 1st place, so I am not too concerned. The supplied charger restores the 'full' LED by the following day. It is an unsophisticated charger and should not be left connected for days after 'full' as there is a risk of overcharging which can slowly kill SLA battery capacity.
Anyway, that is what works for me at the moment.
I personally also feel safer with a stand-alone low voltage supply system than extension leads and 240V adapters outside, particularly in dewy conditions.
good luck with your decisions
cheers
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